Japanese Unexamined Patent Publication (Kokai) No. Showa 60-11706 discloses a pressurized fluid supply system of the type set forth above. FIG. 1 shows the pressurized fluid supply system disclosed in the above-identified publication. A plurality of pressure compensation valves 3 and 13 are connected in parallel to a discharge line pipe 2 of a hydraulic pump 1. Discharge pipes 4 and 14 of respective pressure compensation valves 3 and 13 are provided with direction control valves 5 and 15. The outlet sides of the direction control valves 5 and 15 are connected to actuators 6 and 16. The pressure compensation valves 3 and 13 are constructed to be biased in valve opening direction by a pump discharge pressure and outlet pressures of the direction control valves 5 and 15 and to be biased in valve closing direction by the inlet pressures of the direction control valves and the highest load pressure. With the shown pressurized fluid supply system, it becomes possible to supply pressurized fluid discharged from the pump to respective actuators at a predetermined distribution ratio when a plurality of direction control valves 3 and 13 are operated simultaneously.
However, in the above-mentioned pressurized fluid supply system, it becomes essential to provide a shuttle valve 7 for comparing load pressures of respective actuators and supplying the highest load pressure to the pressure compensation valves. Furthermore, the number of shuttle valves required becomes one less than the number of actuators. Therefore, number of necessary shuttle valves is inherently increased according to increasing of the number of the actuators to be supplied with the pressurized fluid, thus increasing cost.
On the other hand, in the pressurized fluid supply system illustrated in FIG. 1, assuming that the load pressure of the actuator 6 is higher than the load pressure of the actuator 16 among the load pressures generated upon actuation of two actuators 6 and 16, a pressure in a passage 8 is introduced into a passage 9 via the shuttle valve 7 as the maximum load pressure. Subsequently, if the load pressure fluctuates and the load pressure of the actuator 16 becomes higher than the load pressure of the actuator 6, the shuttle valve 7 is switched to connect the passage 9 and a passage 18. Upon this switching, due to blow off of the shuttle valve 7, the pressure in the passage 18 drops, and the pressure in the other passage 8 is blocked. As a result, upon switching of the shuttle valve 7, the actuator 6 transitively causes a natural drop and the natural drop is accelerated.